estimates ATM-related inefficiency based on proxy indicators. Ongoing work has highlighted that further inefficiencies related to all stakeholders may be demonstrated by the use of indicators that are based directly on fuel burn or CO2 emissions as opposed to operational proxies such as time or distance flown. Any new metrics should be measured and monitored according to the interdependency of all the stakeholders involved in the evolution of the flight trajectory and their impact upon fuel efficiency.
As explained in 5.2, discussions have already been triggered on the limitations of existing metrics. The sector should aim to move away from proxy metrics based on additional time or distance flown to those based on actual CO2 emissions. EASA and EUROCONTROL, together with ANSPs, are currently working to identify and develop a suite of metrics that could more accurately measure ATM performance and the benefits from the actions of individual stakeholders.
One such metric being considered, developed by the Network Manager in 2019, is referred to as the Excess Fuel Burn indicator (XFB) and is based on actual operational data and modelled fuel burn 42 or the 5th percentile - XFB5). Based on this indicator, the average excess fuel burn per flight in the Intra-Network Manager (Intra-NM) area in 2019 was estimated to be 8.6% and 11.2% for XFB10 and XFB5 respectively. It should be emphasised that the XFB indicator measures the system inefficiency linked to all stakeholders such as airports, flight planning processes, aircraft operators, ATC and the network itself.. The XFB is the fuel inefficiency on a particular route for a particular aircraft type, compared to a reference based on the best performer on that city pair / aircraft type combination (it can either be the 10th percentile- XFB10
Considerations may still be required to address those situations where optimised flight routings of aircraft operators, may not necessarily align with the NM calculated environmentally optimised trajectory (i.e. modelled lowest fuel burn), and therefore reductions in fuel inefficiency clearly needs further analysis with all involved stakeholders.
43 shows that XFB10 in the Intra-NM Area ranged between 7.8% to 9.8% during 2019. Following the start of the pandemic, the XFB10 fell to between 2 and 5% during 2020 and 2021, finishing at 3.8% at the end of 2021. This demonstrates the network efficiency improvements that could be achieved in low traffic periods if the large number of current airspace restrictions are removed within the current airspace configuration. The figure also illustrates that there may be system constraints that are challenging to remove even when traffic numbers are at a minimum, such as military areas and airport terminal airspace constraints.
Fuel burn per flight can be broken down to demonstrate the impact that flight distance, aircraft operations or aircraft type have on fuel efficiency. In relative percentage terms, XFB10 is higher for the short-haul flights and reduces as the flight distance increases. This is due to longer flights typically spending a higher proportion of their flight time in the more fuel-efficient cruise phase. 44 fuel burn during 2019-2021 for all flights in separate distance bands.shows the actual versus reference
42The 10th percentile (XFB10) reference means in effect that for a city pair / aircraft type combination 90% of flights burnt more fuel than the reference and 10% of flights burnt the equivalent or less fuel.
43Intra-Network Manager (Intra-NM) Area is ECAC plus Morocco and Israel but without Iceland.
44The reference fuel burn is the 10%tile fuel burn